1. Field of the Invention
The present invention relates to a stage, a substrate processing apparatus, a plasma processing apparatus, a control method for the stage, a control method for the plasma processing apparatus, and storage media, and in particular relates to a stage on which a substrate to be processed such as a semiconductor wafer is mounted, and a plasma processing apparatus having the stage therein.
2. Description of the Related Art
A plasma processing apparatus constituting a substrate processing apparatus carries out plasma processing such as etching using plasma on semiconductor wafers as substrates processed for manufacturing semiconductor devices.
Such a plasma processing apparatus has a processing chamber for carrying out the plasma processing, an upper electrode and a lower electrode being provided in the chamber for supplying predetermined RF (radio frequency) power for producing the plasma. The lower electrode also acts as a stage (susceptor) on which each semiconductor wafer is mounted. The stage has an ESC (electrostatic chuck) function of electrostatically attracting (chucking) thereto the semiconductor wafer mounted thereon through application of a predetermined voltage.
Moreover, in such a plasma processing apparatus, before carrying out the plasma processing on a semiconductor wafer, reaction by-products or the like attached to an inner wall of the chamber may be removed by carrying out waferless dry cleaning (WLDC) (see U.S. Pat. No. 6,325,948, for example).
However, for such a plasma processing apparatus, each time the plasma processing or the WLDC is carried out, and furthermore each time a semiconductor wafer is attracted onto the stage, the surface state of the stage changes.
Specifically, reaction by-products comprised of fine particles produced through the plasma processing become attached as deposit to low-temperature portions of the surface of the stage in particular. Moreover, the surface of the stage is roughened (worn away) through the WLDC. Furthermore, when a semiconductor wafer is attracted onto the stage, slight movement occurs while a rear surface of the semiconductor wafer is in contact with the surface of the stage, and hence minute undulations on the surface of the stage are smoothed down.
As a result of the above, the actual area over which the surface of the stage and the rear surface of the semiconductor wafer contact one another changes, and hence the thermal transmission characteristics between the stage and the semiconductor wafer change (i.e. ESC drift occurs). This ESC drift is also affected by the time period (or number of times) of usage of the plasma processing apparatus, for example by the time period for which the RF power has been supplied.
In recent years, as semiconductor devices have become smaller in size, very high processing precision has come to be demanded of plasma processing such as etching. To achieve such high processing precision, it is necessary to make each of the semiconductor wafers subjected to the plasma processing be at the same temperature. However, ESC drift causes the thermal transmission characteristics between the stage and a semiconductor wafer to change as described above, and hence directly affects the temperature of each semiconductor wafer. In a plasma processing apparatus, there is thus a problem that even if the plasma processing such as etching is carried out under the same conditions, for example at the same RF power, for each of the semiconductor wafers, the temperature differs between the semiconductor wafers, and hence the processing precision changes, whereby the semiconductor device yield decreases.